The present invention relates generally to protection of the starter of an internal combustion engine, for example as employed in motor vehicles and military equipment, and, more particularly, for protecting a starter from overheating as a result of cranking for an excessive period of time when the engine is difficult to start.
A particular problem encountered when starting internal combustion engines, particularly for vehicles, is an enormous buildup of heat in the starter windings when the engine is difficult to start and the starter is energized for an excessive period of time. Due to the rapid rate at which heat is generated in the windings and the time required for heat conduction, the windings can become excessively hot to the point of damage even though the temperature of the starter housing is relatively cool.
One previous solution has been to provide thermostatic switches mounted on the starter housing for preventing starter energization when a predetermined temperature is reached. While such switches offer some protection, they are not an entirely reliable means of protection due to the temperature differential between the heat-producing starter windings and housing, and due to variations in ambient temperature.
In an effort to avoid this problem, operators' manuals for some equipment prescribe specific starting procedures, which include instructions to limit cranking time, and to provide adequate cooling off intervals between starter actuations. A typical such specification provides for a two-to-one off-to-on time ratio.
However, dependency upon an operator following instructions, or even necessarily being aware of the instructions, in many instances provides less than satisfactory protection. Accordingly, there exists a need for automatic protection systems which provide greater protection than does a thermostatic switch mounted on the starter housing and which do not rely upon an operator following instructions.
Although not directed to the protection of motor vehicle starters from overheating, of some pertinancy in view of the specific solution of the present invention are certain systems for automatically starting a vehicle at predetermined time such as might be controlled by a clock. Four such systems are disclosed to Stelter U.S. Pat. No. 3,230,401, Corey U.S. Pat. No. 3,325,657, McWhirter U.S. Pat. No. 3,259,753, and Waterhouse U.S. Pat. No. 4,188,931. By way of specific example, in the automatic vehicle starting system of the Waterhouse patent, in the event the engine does not immediately start, the starting sequence is repeated over and over for a certain period of time. In Waterhouse, in order to closely simulate manual automobile starting procedures, and to minimize the likelihood of the automobile battery becoming excessively discharged, the starter motor is for example automatically cranked for thirty seconds ON and the ten seconds OFF, for an overall period of six to eight minutes.